To realize a compact and high-power electric motor, the use of high-Br magnets having a high residual magnetic flux density Br is effective. However, the electric motor using the high-Br magnets has a tendency to have a high magnetic flux density in its core, so that magnetic saturation is more likely to occur.
The occurrence of magnetic saturation leads to an increase in iron loss, causing motor efficiency to be reduced. Due to the occurrence of magnetic saturation, spatial harmonics and temporal harmonics increase in a magnetic flux density distribution, so that torque pulsation increases.
As a method for reducing the increase in iron loss due to magnetic saturation and reducing the torque pulsation due to the increased spatial harmonics and temporal harmonics, there is a method by which magnetic flux-weakening control is performed in an operating region in which a power supply voltage applied to armature windings becomes larger than the sum of a no-load induced voltage and an armature reaction voltage (see Patent Literature 1, for example).